Of the 2,348 miles of streams in Chester County, PADEP periodically assesses 1,394 stream miles using an USEPA-approved assessment methodology to determine if a stream is meeting water quality standards. In the 2020 report, PADEP listed 961 miles of streams in Chester County as impaired, which means they do not meet water quality standards. The list of impaired streams, as well as the list of streams assessed that met the water quality standards, are found in the "2020 Pennsylvania Integrated Water Quality Monitoring and Assessment Report."
Common impairments in Chester County include "siltation due to urban runoff/storm sewers” and "nutrients due to agriculture." In total, there are over two dozen unique impairment categories listed in Chester County. Stream can be listed by PADEP as impaired for two or more reasons if there are multiple impacts that result in the stream not attaining their designated use.